In this article, we report the measurement of underwater aerophobicity, through the captive-bubble method, for different polymeric coatings employed to protect microscale and nanoscale flexible electronic devices for seawater applications. Controlling the morphology and wettability of the coating, in particular with the incorporation of nanoparticles of fluorinated polymers, allows to adjust the hydrophilic/hydrophobic (aerophobic/aerophilic) character of the surface in order to achieve a more insulating and antibiofouling behavior. Morphological analysis (roughness) and wettability measurements in sessile-drop and captive-bubble methods were provided for some properly selected polymeric coatings. We found that parylene C decorated with poly(vinylidene fluoride) nanoparticles at a higher dispersion concentration (5 mg/mL) exhibits the best compromise between morphology, hydrophobicity, and underwater aerophobicity, with sessile-drop water contact angle of 95.1 ± 2.9° and captive-air-bubble contact angle of 133.1 ± 5.9°.

In this work we have compared two different sensing platforms for the detection of morphine as an example of a low molecular weight target analyte. For this, molecularly imprinted polymer nanoparticles (NanoMIP), synthesized with an affinity towards morphine, were attached to an electrochemical impedance spectroscopy (EIS) and a quartz crystal microbalance (QCM) sensor. Assay design, sensors fabrication, analyte sensitivity and specificity were performed using similar methods. The results showed that the EIS sensor achieved a limit of detection (LOD) of 0.11 ng·mL−1, which is three orders of magnitude lower than the 0.19 µg·mL−1 achieved using the QCM sensor. Both the EIS and the QCM sensors were found to be able to specifically detect morphine in a direct assay format. However, the QCM method required conjugation of gold nanoparticles (AuNPs) to the small analyte (morphine) to amplify the signal and achieve a LOD in the µg·mL−1 range. Conversely, the EIS sensor method was labor-intensive and required extensive data handling and processing, resulting in longer analysis times (~30–40 min). In addition, whereas the QCM enables visualization of the binding events between the target molecule and the sensor in real-time, the EIS method does not allow such a feature and measurements are taken post-binding. The work also highlighted the advantages of using QCM as an automated, rapid and multiplex sensor compared to the much simpler EIS platform used in this work, though, the QCM method will require sample preparation, especially when a sensitive (ng·mL−1) detection of a small analyte is needed.